1. Field of the Invention
The present invention relates to an optical disk unit which uses an optical disk having a track guide groove and has a function for getting access to both a land portion and a groove portion of this optical disk. The present invention also relates to a method for controlling an operation of this optical disk unit. The present invention also relates to an optical disk having pregrooves and prepits for tracking formed in different positions of central lines, and an optical disk unit capable of regenerating a prepit of the optical disk and stably performing a tracking operation. The present invention further relates to an optical information recording medium such as an optical disk, an optical card, an optical tape, etc. for recording and regenerating information by using a laser converging beam, and a method for recording and regenerating information by using this optical information recording medium.
2. Description of the Related Art
In the case of an optical disk having a track guide groove, information is generally recorded to any one of a groove portion as the track guide groove and a land portion arranged between groove portions.
In contrast to this, for example, information is recorded to both the land and groove portions to double a recording capacity of the optical disk in Japanese Patent Application Laying Open (KOKAI) No. 4-195939.
In the optical disk, it is necessary to record address information by a prepit in advance every information sector.
In the above proposed optical disk, this prepit is formed in a boundary portion between the land and groove portions. Thus, the same address information is read when an optical pickup tracks the land portion and gets access to the land portion and the optical pickup tracks the groove portion and gets access to the groove portion.
A track number and a sector number are recorded to an address portion. An optical disk unit discriminates object sectors from each other by this information.
In the above construction, the same sector number is provided to each of the land and groove portions. Accordingly, when the optical pickup gets access to the optical disk, the land and groove portions must be correctly discriminated from each other.
A push-pull method using a diffraction phenomenon of light reflected on each of the land and groove portions is often used in tracking control of the optical disk. A tracking error signal obtained by this push-pull method shows a level "0" when there is no tracking shift. The tracking error signal shows a level "+" when there is a tracking shift on one side. The tracking error signal shows a level "-" when there is a tracking shift on the other side. Positive and negative polarities of this tracking error signal in tracking of the optical pickup in the land and groove portions are inverted to each other.
When the tracking error signal shows the level "+", the optical pickup is moved onto an outer circumferential side or an inner circumferential side of the optical disk in a tracking control condition. Tracking operations of the optical pickup in the land and groove portions can be easily switched by changing only this tracking control condition.
However, for example, when the optical pickup concretely tracks the land portion, setting of the above tracking control condition is determined by an electric circuit arranged in an optical disk unit. Accordingly, tracking control conditions in optical disk units are different from each other.
Therefore, for example, there is a setting error possibility that a tracking control condition is set by a user to record information to the land portion, but this information is really recorded to the groove portion. In this case, when information is recorded to the groove portion, this recorded information is destructed.
As mentioned above, in the case of the general optical disk using both the land and groove portions, the optical pickup tends to get access to each of the land and groove portions in error.
In a general known optical disk unit, document information, etc. are recorded onto an optical disk as a digital signal and are regenerated from the optical disk in accordance with necessity. A pregroove for tracking as a guide groove is formed in such an optical disk. Information is recorded to a land between guide grooves.
For example, in an optical disk shown in Japanese Patent Application Laying Open (KOKAI) No. 4-195939, information is recorded to both a land and a pregroove since no recording density can be increased by a recording operation using only the land. A prepit is formed in a central portion between the land and the pregroove. Thus, the same prepit can be read when the pregroove and the land are tracked.
However, when a regenerating operation, etc. of the above optical disk are performed, a portion of the prepit is formed in the pregroove in a prepit region. Therefore, a tracking signal is greatly disturbed when an optical pickup is moved from a pregroove region to the prepit region, or is moved from the prepit region to the pregroove region. Accordingly, the tracking operation becomes unstable so that there is a fear of dislocation of a tracking position of the optical pickup.
Further, the pregroove is formed in the prepit region of the above optical disk so that two laser beams are required to simultaneously form the prepit and the pregroove. Therefore, it is considered to remove the pregroove from the prepit region and form the prepit region by one laser beam. However, in this case, the following problems are caused.
FIG. 1 shows the relation between a tracking signal and a beam locus in a beam scanning direction when the optical pickup tracks a pregroove. As shown in FIG. 1, a tracking signal is greatly disturbed when the optical pickup is moved from a pregroove region to a prepit region, or is moved from the prepit region to the pregroove region. Accordingly, a tracking operation becomes unstable. Therefore, there is a case in which a tracking position of the optical pickup is dislocated from a normal track. Further, the amplitude of a regenerating signal of a prepit shifted from the position of a first prepit beam is greatly different from the amplitude of a regenerating signal of a prepit unshifted from the position of an intermediate prepit beam. In FIG. 1, reference numerals G and L respectively designate a groove and a land.
FIG. 2 shows the relation between switching timing of tracking polarities and a beam locus in a beam scanning direction when the optical pickup tracks the land. As shown in FIG. 2, it is necessary to switch the tracking polarities in pregroove and prepit regions at a land tracking time so as to read the same prepit in a pregroove G and a land L. If no tracking polarities are switched, the optical pickup is separated from a desirable prepit. In this case, each of the tracking polarities shows a tracking operation at a zero crossing point of a difference signal (a tracking signal) shown in each of FIGS. 16 and 17 in a rightward or leftward rising direction.
In a general known optical information recording medium, guide grooves each having a depth of about 1/8 times a wavelength of recorded and regenerated light are formed on a surface of a transparent disk substrate. A prepit series is formed in a land between these guide grooves. A light absorption reflective recording film is formed on this prepit series and information can be recorded to this light absorption reflective recording film by a laser converging beam. In this recording medium, the laser converging beam is diffracted by a diffracting action of a guide groove. A tracking shift is detected by detecting a distribution of light reflected on this groove. A tracking operation is controlled on the basis of the tracking shift. Further, irregular prepit information is read and a recording pit is formed in the recording film in association with the prepit information.
However, in the optical information recording medium of such a type, only one of the groove and the land can be used to perform the tracking operation. Therefore, it is difficult to increase a recording density of information. The tracking operation can be performed in the groove or the land by only inverting a tracking polarity. However, when the prepit series is located in only the land as mentioned above, no prepit having recorded address information, etc. can be read by tracking the groove. Therefore, no additional recording pit can be formed in association with the prepit information so that no information recording density can be increased.
To solve this problem, inventors of this application proposed a novel optical information recording medium in Japanese Patent Application Laying Open (KOKAI) No. 4-195939. As shown in FIG. 3, this recording medium has a groove 103 and a series of prepits 104 for tracking. When a groove clearance as a track pitch is set to P, the prepit series is formed such that a central line of the prepit series is approximately shifted from that of the groove by P/4 on one of left-hand and right-hand sides. An unillustrated light absorption reflective optical recording film is formed on an information recording face of this recording medium. A laser converging beam 106 is irradiated onto this optical recording film. While an intermediate portion of the groove 103 or the land 102 is tracked, the above prepit series is regenerated and information is recorded on the basis of this regeneration. In FIG. 3, reference numerals 101 and 105 respectively designate a disk substrate and a recording pit.
However, the following problems to be improved are caused with respect to the optical information recording medium proposed in the above Japanese laid-open patent and a method for recording and regenerating information by using this optical information recording medium.
(1) As illustrated in FIG. 3 showing the recording medium, the prepit series is located between the groove and the land so that a prepit has an asymmetrical shape. When the tracking operation is performed between the groove and the land, an offset voltage is generated with respect to a push-pull signal. Therefore, it is difficult to accurately perform the tracking operation along the prepit series.
(2) As mentioned above, the prepit has an asymmetrical shape and a considerably complicated sectional shape. Therefore, when a polycarbonate substrate (called a PC substrate in the following description) manufactured by an injection molding method is used as a substrate of the recording medium, no prepit shape of a stamper can be accurately transferred to the substrate when this substrate is manufactured. As a result, there is a possibility of an error in regeneration of preformat information constructed by the prepit series because of a transfer defect. Further, no information can be accurately recorded to a data region constructed by a groove and a land adjacent to the prepit series.
(3) Further, as shown in FIG. 3, a groove is adjacent to a prepit so that an amount of reflected light is greatly reduced in comparison with a case in which the prepit is independently formed. As a result, there is a problem that the amplitude of a signal of the prepit series optically obtained from the prepit by using the laser converging beam is small.